This application is in response to NIMH Program Announcement PA 99-007 for micro-imaging the brain and other parts of the nervous system. It is also consistent with NIH's recent announcement of animal imaging as a key new focus. The ultimate goal of the proposed effort is to develop a small, tomographic gamma camera with in vivo imaging capabilities that allow functional quantitative analysis of animal brain images. The proposed camera will be used with recently developed gamma-ray emitting agents most suitable for SPECT to achieve unprecedented spatial and energy resolution through the use of solid-state photodetector technology and innovative geometrical design. The device developed from this proposal will offer researchers the ability to extract far more accurate quantitative information from animal subjects than is currently possible with whole body SPECT systems on the market, or with autoradiographic techniques, which require sacrificing the subject. The proposed camera would be useful to a large number of researchers interested in understanding basic disease processes, and developing tools for diagnosis and therapy. The objective in Phase I will be to construct a detector module with high density readout electronics that allows seamless tiling of many modules into a larger detector unit. The performance goals of the detector are: a module size of approximately 50 mm x 50 mm with a nominal pixel size of 1 mm2, an intrinsic spatial resolution of between 0.5 and 1.5 mm FWHM, and a spectral resolution of 6% to 8% FWHM for 140 keV gamma-rays. The optimal collimation technique(s) for the intended applications shall also be determined during Phase I, and at least one prototype collimator will be fabricated and tested. Tomographic reconstruction algorithms appropriate for this design and application will also be investigated during the first phase of the project. PROPOSED COMMERCIAL APPLICATION: The Phase I and II development will lead to a new generation of SPECT systems expected to combine significant resolution enhancement with lower cost by utilizing new silicon technologies which need only low cost silicon planar processing and allow integration of electronics with the detector. In the third phase we will commercialize dedicated clinical tomographic imagers for microimaging of animals, based on the Phase I and II efforts. There are large commercial market opportunities in the animal imaging area as well and potential for new commercial systems for humans.